This invention relates generally to the rendering of latent electrostatic images visible. More particularly, the invention relates to a method and apparatus for commutating power to the outer surface of a developer or toner delivery member.
The invention can be utilized in the creation of powder images through the use of xerography. In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a photoreceptor. The photoreceptor comprises a charge retentive surface. A uniformly charged photoreceptor is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves latent charge patterns on the imaging surface corresponding to the areas not exposed by radiation.
This charge pattern is made visible by developing it with toner. The toner is generally a colored powder which adheres to the charge pattern by electrostatic attraction.
The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed by suitable fusing techniques.
A common device for developing powder images formed on a charge retentive surface such as a photoreceptor comprises a magnetic brush toner delivery roll. One such toner delivery device comprises a magnet structure which is stationarily supported using a magnet assembly shaft. A bearing supported by the shaft, in turn, rotatably supports a rotatable shell or tube. Creating a reliable electrical contact to the shell/tube of a magnetic development roll has traditionally required the use of bearings with electrically conductive grease when making the electrical contact through the magnet assembly shaft. Conductive greases cost more than standard greases and do not lubricate as well.
Another type of magnetic brush developer roll utilizes a rotary magnet and shaft assembly in combination with a stationarily supported shell or tube. In order to establish an electrostatic field in the development in this type of developer roll structure, a brush or spring type contact engages the magnetic drive roll shaft. This type of arrangement is subject to brush or spring contact failure due to contamination and potential damage during manufacture and/or servicing. Also, fibers loosened from a contact brush can short out corona devices and have a adverse affect on if they contact the photo receptor.